Study On Temporal And Spatial Variation Of Soil Organic Carbon Stocks And Its Dominating Factors In Cropland

Soil organic carbon (SOC) stocks and its dynamic variation have a strong impact on theglobal C cycle because it can be a major source or sink for atmospheric CO2. SOC stock incropland plays an important role in global C cycle, mitigating greenhouse gas emissions,improving crop production, and protecting the environment. Therefore, to study SOC stock incropland and its temporal and spatial variation, carbon sequestration potential and influencefactors is essential to understand the global C cycle better, to estimate the C sink capacity of soil,and to establish soil C sequestration programs.SOC stocks in cropland with high temporal and spatial variation can be attribute to thecombined influence of natural factors and human activities such as climate condition, soilproperties, fertilizer applications, straw returning and crop rotation systems, besides these factorshave different influence vary with the different research area and scale. In this context, based onthe soil sample data from the Second National Soil Survey of China, as well as the soil sampledata and the formula fertilization by soil testing collected in2010, we took the typical area ofChengdu Plain (Xindu District and Pi County) as study areas and mainly researched the temporaland spatial variation of SOC stocks in cropland topsoil and its dominating factors in typical areaof Chengdu Plain in recent30years. The main research conclusions are as follows:1. Spatial distribution maps of SOCD show that the significant difference of the SOCDtemporal and spatial distribution among two periods in study area. SOCD of the typical area wasuniversally low in1980, with the northwest and central areas had higher SOCD levels, whereassoutheast area had lower levels and southwest and northwest areas contained low levels whichoccupied smaller area. the distribution map also showed a significant increasing trend of SOCDin the typical area in2010, with SOCD levels in eastern areas was higher than that in the westernareas, the SOCD level was low only in some local areas. The total topsoil SOC stocks in croplandof the typical area was2.89Tg (1Tg=106t) in1980, and3.11Tg in2010. In recent30years, theSOC stocks in cropland soils of the typical area increased by0.22Tg.2.The single factor influence of SOCD variation analysis showed that paddy soilsignificantly effected on SOCD variation. The different SOCD types followed a decreasing orderof Gleyed> Hydeomophic> Submergenic> Percogenic. The increment of Hydeomophic paddysoil and Submergenic paddy soil’s SOC stocks were greater than other types significantly, whichgave the greatest contribution to carbon sequestration in agricultural soil. Soil parent materialshad a marked impact on SOCD variation; the increment of SOCD in Chengdu Clay soils wasobviously higher than other parent materials, while the increment of SOCD in Grey-brownalluvium parent materials was the smallest. The influence of soil texture on SOCD occupied animportant position, the different types followed a decreasing order of silty clay> silty clay loam> silt loam> sandy loam in SOCD. Moreover, statistically significant positive correlation between clay content and SOCD, and negative correlation between silt content and SOCD wereobserved at the different times. This indicated that SOCD was increased with the increase of claycontent and decreased with the increase of silt content. Soil total nitrogen had significant positivecorrelation with SOCD, and soil total potassium content had significant negative correlation withSOCD, while total phosphorus content and pH had relatively little and unstable effect on SOCD.Crop rotation systems had a significant effect on SOCD variation, and wheat-rice rotationsystems had higher SOCD levels than other crop rotation systems.3. Dominating factors of SOCD variation were different in different periods. The unitedexplanatory ability of paddy soil subgroups, soil texture, soil parent materials, pH, totalphosphorus content and crop rotation systems to SOCD variability was39.8%in1980, herepaddy soil subgroups(16.5%), soil texture (12.3%)and pH (6.4%) were the dominating factors.While the united explanatory ability of soil texture, total potassium content, paddy soil subgroups,soil parent materials and crop rotation systems to SOCD variability was54.6%in2010, here soiltexture(25.0%), total potassium content(16.1%), paddy soil subgroups (11.7%) were thedominating factors of SOCD variation. Soil properties occupied the leading position ininfluencing the SOCD variation at different times, and the influence of crop rotation systems onSOCD variation was less than soil properties because of its lower explanatory ability.